Optimisation using experimental designs of the sample pretreatment: application to the control of the organotins in sewage sludge by GC-FPD

The optimisation of the simultaneous extraction of the butyl- and phenyltin s from sewage sludge and their derivatization using sodium tetraethylborate (NaBEt4) are reported. The methodology of experimental designs was used wh ich allowed the evaluation of the influence of eight analytical parameters on the peak areas (S) and decomposition (D) of triphenyltin (according to i ts poor stability). The stirring times during extraction and derivatization as well as the NaBEt4 amount were found the most important factors. The op timal operating conditions were determined by modelling S and D. Several sa mples of urban sewage sludge were analysed and results compared with those obtained by other analytical methods, in order to verify the convenience of the optimised method.